This is a large and important cache of letters that sparked Merton's interest in Sufism. Included are original signed letters by Aziz, and carbon copies or photocopies of letters by Merton. Only Merton's side of the correspondence has yet been fully published and can be found in «The Hidden Ground of Love». Selection from Aziz's side of the correspondence can be found in «Merton and Sufism». Also in this group of records can be found correspondence between the Merton Center and Nicholas Heer in regards to obtaining some correspondence between Heer and Aziz. This correspondence dating from 1959 through 1962 is included in this collection.